diff --git a/src/muz/spacer/spacer_cluster.cpp b/src/muz/spacer/spacer_cluster.cpp
index b03562b12..fac3a920f 100644
--- a/src/muz/spacer/spacer_cluster.cpp
+++ b/src/muz/spacer/spacer_cluster.cpp
@@ -378,7 +378,7 @@ void lemma_cluster_finder::cluster(lemma_ref &lemma) {
                                    << pattern << "\n"
                                    << " and lemma cube: " << lcube << "\n";);
 
-    for (const lemma_ref &l : neighbours) {
+    for (auto l : neighbours) {
         SASSERT(cluster->can_contain(l));
         bool added = cluster->add_lemma(l, false);
         (void)added;